(Binary Clone Detection) Compute window overlaps

For each pair of functions that are in a similarity cluster,
we compute the number of bytes that are in the similar windows
of both functions, and the ratio of those numbers with the total
size of the functions, taking into account:
  * functions need not be contiguous in the specimen address space
  * two instructions can overlap in the address space
  * instructions do not always occur in address order within a function
  * windows are likely to overlap with each other in a function
(Binary Simulator) Fixed function byte counts for clone detection